1. Field of the Invention
This invention relates generally to packaging of semiconductors, and in particular, to a leadframe semiconductor package.
2. Description of the Prior Art
Leadframe semiconductor packages are well known in the art. A conventional leadframe typically includes a plurality of metal leads temporarily held together in a planar arrangement about a central region during package manufacture by a rectangular frame. A die pad is supported in the central region by a plurality of tie bars that attach to the frame. The leads extend from a first end integral with the frame to an opposite second end adjacent to, but spaced apart from, the die pad.
During package manufacture, a semiconductor die is attached to the die pad. Wire-bonding pads on the die are then connected to selected ones of the inner ends of the leads by fine, conductive bonding wires to convey power, ground or signals between the die and the leads. A protective body of an epoxy resin is molded over the assembly to enclose and seal the die, the inner ends of the leads, and the wire bonds against harmful environmental elements. The rectangular frame and the outer ends of the leads are left exposed outside of the body, and after molding, the frame is cut away from the leads and discarded, and the outer ends of the leads are appropriately formed for interconnection of the package with an external printed circuit board.
One known type of the leadframe semiconductor packages is the so-called exposed die pad (E-pad) leadframe package that exposes the bottom surface of the die pad to the outside of the encapsulation body. The exposed die pad acts as a heat sink and can improve the heat-dissipation efficiency. Typically, the exposed die pad is electrically connected to a ground plane of the external printed circuit board.
It has been found that the E-pad leadframe package is subject to attacks of moisture. To avoid reliability problems due to moisture attacks and delamination along the plastic body-metal interface, the ground wires extended from the ground pads of the semiconductor die are not directly bonded onto the surface of the die pad, but instead the ground wires are bonded to a rectangular ring shaped ground bridge bar that encircles the die pad at different downset planes. Typically, the ground bridge bar is supported by tie bars that connected with the die pad.
However, the prior art leadframe package with such ground bridge bar configuration has a shortcoming of that the analog and digital ground wires randomly bonded together onto the ground bridge bar can result in noise or ground coupling, which is also known as water wave effects in TV systems. Another shortcoming is that the ground bridge bar is vulnerable to twist and deform, leading to poor bonding strength. It is therefore desirable to provide an improved leadframe package structure that may eliminate the aforesaid digital and analog ground coupling and the water wave effects in TV systems.